Overlay mark design for electron beam overlay

Abstract

The present disclosure provides a target and a method of performing overlay measurements on a target. The target includes an array of cells comprising a first cell, a second cell, a third cell, and a fourth cell. Each cell includes a periodic structure with a pitch. The periodic structure includes a first section and a second section, separated by a first gap. The target further includes an electron beam overlay target, such that electron beam overlay measurements, advanced imaging metrology, and/or scatterometry measurements can be performed on the target.

What is claimed is: 
     
       1. A target comprising:
 an array of cells comprising a first cell, a second cell, a third cell, and a fourth cell, each comprising a periodic structure with a pitch, wherein the periodic structure includes a first section and a second section, separated by a first gap; and 
 an electron beam overlay target disposed in a center of the array of cells comprising the first cell, the second cell, the third cell, and the fourth cell. 
 
     
     
       2. The target of  claim 1 , wherein the first cell, the second cell, the third cell, and the fourth cell are arranged having rotational symmetry. 
     
     
       3. The target of  claim 1 , wherein the periodic structure of each cell further includes a third section separated by a second gap. 
     
     
       4. The target of  claim 1 , wherein the periodic structure of the first cell has a first cell height along the first axis and a first cell width along the second axis, the periodic structure of the second cell has a second cell height along the second axis and a second cell width along the first axis, the periodic structure of the third cell has a third cell height along the second axis and a third cell width along the first axis, and the periodic structure of the fourth cell has a fourth cell height along the first axis and a fourth cell width along the second axis, and wherein the first cell width is greater than the second cell height, the second cell width is greater than the third cell height, the third cell width is greater than the fourth cell height, and the fourth cell width is greater than the first cell height. 
     
     
       5. The target of  claim 1 , wherein the periodic structure of the first cell has a first cell height along the first axis and a first cell width along the second axis, the periodic structure of the second cell has a second cell height along the second axis and a second cell width along the first axis, the periodic structure of the third cell has a third cell height along the second axis and a third cell width along the first axis, and the periodic structure of the fourth cell has a fourth cell height along the first axis and a fourth cell width along the second axis, and wherein the first cell width is equal to the second cell height, the second cell width is equal to the third cell height, the third cell width is equal to the fourth cell height, and the fourth cell width is equal to the first cell height. 
     
     
       6. The target of  claim 1 , wherein part of the electron beam overlay target is a plurality of nested polygonal shapes disposed inside each other that define a center hollow area. 
     
     
       7. The target of  claim 6 , wherein the interconnected polygonal shapes are squares. 
     
     
       8. The target of  claim 6 , wherein the periodic structure of each cell have a first height and a second height larger than the first height, and wherein the periodic structure with the second height is disposed adjacent the electron overlay target. 
     
     
       9. The target of  claim 6 , wherein the second section of the periodic structure of each cell has a second height and a third height less than the second height, and wherein the periodic structure with the third height is disposed adjacent the electron overlay target. 
     
     
       10. A method of performing overlay measurements on the target of  claim 1  using a semiconductor metrology tool. 
     
     
       11. A target comprising:
 an array of cells comprising a first cell, a second cell, a third cell, and a fourth cell, each comprising a periodic structure with a pitch, wherein the periodic structure includes a first section and a second section, separated by a first gap; and 
 a plurality of electron beam overlay targets disposed at an edge of the first cell, the second cell, the third cell, and the fourth cell, wherein each of the electron beam overlay targets includes a body, a plurality of segments extending from the body, and a connecting segment which connects ends of the plurality of segments. 
 
     
     
       12. The target of  claim 11 , wherein the plurality of the electron beam overlay targets are disposed at the edge of the first cell, the second cell, the third cell, and the fourth cell adjacent to the first section of the periodic structure. 
     
     
       13. The target of  claim 11 , wherein the plurality of the electron beam overlay targets are disposed at the edge of the first cell, the second cell, the third cell, and the fourth cell adjacent to the second section of the periodic structure. 
     
     
       14. The target of  claim 13 , wherein the plurality of the electron beam overlay targets are disposed at the edge of the first cell, the second cell, the third cell, and the fourth cell adjacent to the first gap. 
     
     
       15. The target of  claim 11 , wherein the periodic structures further includes a second pitch between groups of a plurality of periodic structures at the pitch, wherein the second pitch is larger than the first pitch. 
     
     
       16. A method of performing overlay measurements on the target of  claim 11  using a semiconductor metrology tool. 
     
     
       17. A target comprising:
 an array of cells comprising a first cell, a second cell, a third cell, and a fourth cell, each comprising a periodic structure with a pitch, wherein the periodic structure includes a first section and a second section, separated by a first gap; and 
 a plurality of electron beam overlay targets, wherein each of the electron beam overlay targets includes a plurality of segments extending from two sides of a body, wherein the body is disposed between pairs gratings in the first section and the second section of the periodic structure and the plurality of segments are disposed on the pairs of gratings in the first and second section adjacent to the body. 
 
     
     
       18. The target of  claim 17 , wherein the plurality of electron beam overlay targets are disposed between pairs of gratings at ends of the first section and the second section of the periodic structure of each cell. 
     
     
       19. The target of  claim 17 , wherein the plurality of electron beam overlay targets are disposed between each pair of gratings of the first section and the second section of the periodic structure of each cell. 
     
     
       20. A method of performing overlay measurements on the target of  claim 16  using a semiconductor metrology tool.